U.S. patent number 8,033,646 [Application Number 13/010,815] was granted by the patent office on 2011-10-11 for liquid drop dispenser with movable deflector.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Joseph Jech, Jr., Michael J. Piatt, Yonglin Xie, Qing Yang.
United States Patent |
8,033,646 |
Xie , et al. |
October 11, 2011 |
Liquid drop dispenser with movable deflector
Abstract
A liquid dispenser includes a liquid supply channel and a liquid
ejector channel that includes an outlet opening. A liquid supply
provides a flow of a pressurized liquid through the liquid ejector
channel from the liquid supply channel. The pressurized liquid has
a momentum as the liquid moves through the liquid ejector channel.
A liquid return channel receives the liquid after the liquid passes
through the liquid ejector channel. A diverter member forms at
least a portion of a wall of the liquid ejector channel. A portion
of the diverter member is selectively movable away from the liquid
flowing through the liquid ejector channel. The momentum of the
liquid causes some of the liquid to be diverted through the outlet
opening when the portion of the diverter member is moved away from
the liquid flowing through the liquid ejector channel.
Inventors: |
Xie; Yonglin (Pittsford,
NY), Piatt; Michael J. (Dayton, OH), Jech, Jr.;
Joseph (Webster, NY), Yang; Qing (Pittsford, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
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Family
ID: |
40522862 |
Appl.
No.: |
13/010,815 |
Filed: |
January 21, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110109698 A1 |
May 12, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12024360 |
Feb 1, 2008 |
7914121 |
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Current U.S.
Class: |
347/54 |
Current CPC
Class: |
B41J
2/04 (20130101); B41J 2/14427 (20130101); B41J
2202/12 (20130101); B41J 2202/15 (20130101) |
Current International
Class: |
B41J
2/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 436 509 |
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Jul 1991 |
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EP |
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0436509 |
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Jul 1991 |
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EP |
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95/10415 |
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Apr 1995 |
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WO |
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WO 95/10415 |
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Apr 1995 |
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WO |
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Other References
Wikibedia Article-Convex, Paragraph 1. cited by other.
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Primary Examiner: Luu; Matthew
Assistant Examiner: Solomon; Lisa
Attorney, Agent or Firm: Zimmerli; William R.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation application of U.S. application Ser. No.
12/024,360 filed Feb. 1, 2008 now U.S. Pat. No. 7,914,121.
Reference is made to commonly assigned, co-pending U.S. patent
application Ser. No. 13/010,820, which is a continuation
application of U.S. patent application Ser. No. 11/944,658, filed
in the name of Eastman Kodak Company on Nov. 26, 2007.
Claims
The invention claimed is:
1. A liquid dispenser comprising: a liquid ejector channel
including an outlet opening; a liquid supply channel; a liquid
return channel; a liquid supply that provides a flow of a
pressurized liquid from the liquid supply channel through the
liquid ejector channel and past the outlet opening to the liquid
return channel, the pressurized liquid having a momentum as the
liquid moves through the liquid ejector channel and past the outlet
opening; and a diverter member forming at least a portion of a wall
of the liquid ejector channel, a portion of the diverter member
being selectively movable away from the liquid flowing through the
liquid ejector channel, the momentum of the liquid causing some of
the liquid to be diverted through the outlet opening when the
portion of the diverter member is moved away from the liquid
flowing through the liquid ejector channel.
2. The liquid dispenser of claim 1, wherein the liquid flows from
the liquid supply channel to the liquid return channel through the
liquid ejector channel when the portion of the diverter member is
not moved away from the liquid flowing through the liquid ejector
channel.
3. The liquid dispenser of claim 1, wherein the diverter member
forms a convex surface along which liquid remains attached when the
portion of the diverter member is moved away from the liquid
flowing through the liquid ejector channel.
4. The liquid dispenser of claim 1, wherein the liquid dispenser
has a response frequency greater than 400 kHz.
5. The liquid dispenser of claim 1, wherein the diverter member is
a thermal bimorph transducer.
6. The liquid dispenser of claim 1, wherein the diverter member is
a piezoelectric transducer.
7. The liquid dispenser of claim 1, wherein the diverter member is
an electrostatic transducer.
8. The liquid dispenser of claim 1, wherein the diverter member is
a magnetic transducer.
9. The liquid dispenser of claim 1, further comprising: a
controller configured to intermittently move the diverter member
away from the liquid flowing through the liquid ejector channel.
Description
FIELD OF THE INVENTION
This invention relates generally to the field of fluid dispensers
and particularly, but not exclusively, to an on-demand dispenser of
very small quantities of liquid. The invention is particularly
useful in digitally controlled ink jet printing devices wherein
droplets of ink are ejected from nozzles in a printhead toward a
print medium.
BACKGROUND OF THE INVENTION
Traditionally, color ink jet printing is accomplished by one of two
technologies, referred to as drop-on-demand and continuous stream
printing. Both technologies require independent ink supplies for
each of the colors of ink provided. Ink is fed through channels
formed in the printhead. Each channel includes a nozzle from which
droplets of ink are selectively extruded and deposited upon a
medium. Typically, each technology requires separate ink delivery
systems for each ink color used in printing. Ordinarily, the three
primary subtractive colors, i.e. cyan, yellow and magenta, are used
because these colors can produce up to several million perceived
color combinations.
In drop-on-demand ink jet printing, such as shown in U.S. Pat. No.
6,065,825, ink droplets are generated for impact upon a print
medium using a pressurization actuator (thermal, piezoelectric,
etc.). Selective activation of the actuator causes the formation
and ejection of a flying ink droplet that crosses the space between
the printhead and the print medium and strikes the print medium.
The energy to propel such droplets from the ejector comes from the
pressurization activator associated with that ejector. The
formation of printed images is achieved by controlling the
individual formation of ink droplets at each ejector as the medium
is moved relative to the printhead.
Conventional drop-on-demand ink jet printers utilize a
pressurization actuator to produce the ink jet droplet from the
nozzles of a printhead. Typically, one of two types of actuators is
used including heat actuators and piezoelectric actuators. With
heat actuators, a heater, placed at a convenient location, heats
the ink. This causes a quantity of ink to phase change into a
gaseous steam bubble that raises the internal ink pressure
sufficiently for an ink droplet to be expelled. With piezoelectric
actuators, an electric field is applied to a piezoelectric material
possessing properties that create a pulse of mechanical movement
stress in the material, thereby causing an ink droplet to be
expelled by a pumping action. The most commonly produced
piezoelectric materials are ceramics, such as lead zirconate
titanate, barium titanate, lead titanate, and lead metaniobate.
The volume of ink ejected by such nozzles is determined by the
quantity of fluid ejected at each actuation of the drive mechanism,
the velocity with which the fluid is ejected, and the rate of
ejection. For a given geometry of the chamber, the pressure at
which the fluid is supplied to the chamber and the operational
characteristics of the drive mechanism determine all of those
parameters. By increasing the supply pressure and the displacement
of the drive mechanism in the forward stroke, either independently
or as combined parameters, the ejection quality can be increased.
However, if the supply pressure is to be increased substantially
above the pressure at the outlet of the jet (which in printheads is
generally atmospheric pressure), the fluid column cannot be
contained in the chamber during the off periods of the dispenser
i.e. during periods when no fluid is to be ejected from that
particular jet. Fluid will therefore drip out of the jet during
those periods. Hence, the most influential parameter in achieving
high-quality drop on demand in these known dispensers is the
maximum obtainable displacement of the drive mechanism, which is
clearly limited.
The second technology, commonly referred to as continuous stream or
continuous ink jet printing, uses a pressurized ink source for
producing a continuous stream of ink droplets from each ejector.
Typically, the pressurized ink is in fluidic contact with all the
ejectors through a common manifold. The energy to propel droplets
from the ejectors comes from the pressurization means pressurizing
the manifold, which is typically a pump located remotely from the
printhead. Conventional continuous ink jet printers utilize
electrostatic charging devices that are placed close to the point
where a filament of working fluid breaks into individual ink
droplets. The ink droplets are electrically charged and then
directed to an appropriate location by deflection electrodes having
a large potential difference. When no print is desired, the ink
droplets are deflected into an ink-capturing mechanism (catcher,
interceptor, gutter, etc.) and either recycled or discarded. When
printing is desired, the ink droplets are not deflected and allowed
to strike a print media. Alternatively, deflected ink droplets may
be allowed to strike the print media, while non-deflected ink
droplets are collected in the ink capturing mechanism.
Other methods of continuous ink jet printing employ air flow in the
vicinity of ink streams for various purposes. For example, U.S.
Pat. No. 3,596,275 issued to Sweet in 1978 discloses the use of
both collinear and perpendicular air flow to the droplet flow path
to remove the effect of the wake turbulence on the path of
succeeding droplets. This work was expanded upon in U.S. Pat. No.
3,972,051 to Lundquist et al., U.S. Pat. No. 4,097,872 to Hendriks
et al. and U.S. Pat. No. 4,297,712 to Lammers et al. in regards to
the design of aspirators for use in droplet wake minimization. U.S.
Pat. No. 4,106,032, to Miura and U.S. Pat. No. 4,728,969 to Le et
al. employ a coaxial air flow to assist jetting from a
drop-on-demand type head.
While this method does not rely on electrostatic means to affect
the trajectory of droplets, it does rely on the precise control of
the break off points of the filaments and the placement of the air
flow intermediate to these break off points. Such a system is
difficult to control and to manufacture. Furthermore, the physical
separation or amount of discrimination between the two droplet
paths is small further adding to the difficulty of control and
manufacture. As such, these printheads suffer from a lack of
precise control of the placement of drops on the print medium,
which can produce visible image artifacts.
One problem associated with ink jet printers in general and such
printers employing gas or air flows in particular is the drying of
the ink. Ink drying in the vicinity of the printhead nozzles can
lead to spurious droplet trajectories and nozzle clogging. In some
cases, the evaporation of volatile ink solvents from the droplets
as they fly through the air can increase the viscosity of the ink
captured by the gutter, thereby causing difficulties during the ink
recycling operation when the recycled ink is passed through a
filter. This last problem becomes particularly difficult if the
loss of solvent in the ink is large enough to cause the pigments in
the ink to coagulate. Yet another problem associated with the
guttering of inks is that the gutter is provided with a negative
pressure, and is thereby subject to sucking wind, dirt, and frothy
mist into the ink to be recycled.
European Patent Application No. EP-A-0436509 describes a fluid
dispenser comprising a main chamber to which fluid is fed under
pressure and a pair of outlet channels. A dispensing outlet channel
leads to a dispensing outlet, whilst a recirculation outlet channel
conducts the fluid back into the fluid supply. In use, the fluid
normally veers towards the recirculation outlet channel leading
back to the fluid supply. When a drop of fluid is to be dispensed,
a driver device is momentarily energized so that the fluid flow
switches over to the dispensing outlet channel. As soon as the
required quantity of fluid has been dispensed, the flow is switched
back to the recirculation channel by energization of a second
driver device, so that the fluid again circulates back to the fluid
supply. A disadvantage of the fluid dispenser is that two driver
devices are required at each nozzle. Another disadvantage is that
each nozzle requires a large footprint on the printhead to
accommodate the pair of driver devices.
WO 95/10415 discloses a fluid dispenser comprising a supply
channel; fluid supply means for feeding said main fluid to the
supply channel under pressure; a first fluid path along which the
main fluid is fed from the supply channel; a second fluid path
including a fluid dispensing outlet; a control channel containing
control fluid and having a control outlet adjacent the first fluid
path, and means for changing pressure in said control fluid such
that a wave front is formed in the main fluid and a droplet of said
main fluid is dispensed from the fluid dispensing outlet. The main
fluid flow follows the first fluid path due to Coanda effect except
when diverted by change of pressure of the control fluid. While
this fluid dispenser overcomes the need for two driver devices in
European Patent Application No. EP-A-0436509, droplets to be
dispensed are unsupported as they depart from the main fluid flow
to exit the fluid dispensing outlet. As such, these printheads
suffer from a lack of precise control of the placement of drops on
the print medium, which can produce visible image artifacts. U.S.
Pat. No. 4,345,259 is quite similar to WO 95/10415, and is cited
here for the sake of completeness.
SUMMARY OF THE INVENTION
According to a feature of the present invention, a liquid dispenser
includes a liquid supply channel, a liquid supply adapted to feed a
stream of liquid through the supply channel, a liquid return
channel adapted to receive liquid from the supply channel, a liquid
dispensing outlet opening, and a diverter member forming at least a
portion of a wall of the liquid supply channel, said diverter
member being selectively movable to form a convex surface along
which liquid remains attached, thereby to divert droplets from the
supply channel through the dispensing outlet opening by Coanda
effect.
According to another feature of the present invention, the liquid
flows from the liquid supply channel to the liquid return channel
by Coanda effect when not diverted.
According to still another feature of the present invention, the
motion of the diverter member is substantially orthogonal to and
opposes the direction of liquid flow, so that energy associated
with moving the diverter member imparts no energy to the diverted
droplets.
According to yet another feature of the present invention, the
energy associated with moving the diverter member is less than 100
nJ per pL droplet volume. In some embodiments of the present
invention, the energy associated with moving the diverter member is
less than 10 nJ per pL droplet volume.
According to yet another feature of the present invention, the
liquid dispenser has a response frequency greater than 400 kHz. The
diverter member may be a thermal bimorph transducer, a
piezoelectric transducer, an electrostatic transducer, a magnetic
transducer, or other suitable member.
According to another feature of the present invention, a liquid
dispenser includes a liquid supply channel and a liquid ejector
channel that includes an outlet opening. A liquid supply provides a
flow of a pressurized liquid through the liquid ejector channel
from the liquid supply channel. The pressurized liquid has a
momentum as the liquid moves through the liquid ejector channel. A
liquid return channel receives the liquid after the liquid passes
through the liquid ejector channel. A diverter member forms at
least a portion of a wall of the liquid ejector channel. A portion
of the diverter member is selectively movable away from the liquid
flowing through the liquid ejector channel. The momentum of the
liquid causes some of the liquid to be diverted through the outlet
opening when the portion of the diverter member is moved away from
the liquid flowing through the liquid ejector channel.
According to another feature of the present invention, the liquid
flows from the liquid supply channel to the liquid return channel
through the liquid ejector channel when the portion of the diverter
member is not moved away from the liquid flowing through the liquid
ejector channel.
According to another feature of the present invention, the diverter
member forms a convex surface along which liquid remains attached
when the portion of the diverter member is moved away from the
liquid flowing through the liquid ejector channel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view of a dispenser made in accordance
with a preferred embodiment of the present invention;
FIG. 2 is a schematic plan view of the dispenser of FIG. 1 in its
"active" mode;
FIG. 3 is a detailed view of the dispenser of FIG. 1; and
FIGS. 4-6 are detail views of a portion of the dispenser of FIG. 1
showing three preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present description will be directed in particular to elements
forming part of, or cooperating more directly with, apparatus in
accordance with the present invention. It is to be understood that
elements not specifically shown or described may take various forms
well known to those skilled in the art.
With reference to FIG. 1, a dispenser 10 according to a preferred
embodiment of the present invention is formed from a semiconductor
material (silicon, etc.) using known semiconductor fabrication
techniques (CMOS circuit fabrication techniques, micro-electro
mechanical structure (MEMS) fabrication techniques, etc.). However,
it is specifically contemplated and therefore within the scope of
this disclosure that dispenser 10 may be formed from any materials
using any fabrication techniques conventionally known in the
art.
A supply channel 12, which extends from a supply chamber 14,
carries a liquid pressurized by a pump 16 to be dispensed, on
demand, from an outlet opening 18. The liquid may be, for example,
a printing ink. The liquid flows through ejector channel 17; and,
when no drops are being ejected, flows entirely below outlet
opening 18 at a velocity substantially equal to the velocity of the
drops to be ejected from outlet opening 18 when fluid is being
dispensed, as described below. The energy to sustain this flow is
provided by pump 16 at all times.
A diverter member 20 is selectively movable from a passive position
illustrated in FIG. 1 to an active position as shown in FIG. 2 by a
controller 22. When diverter member 20 is in its passive, FIG. 1
position, liquid flowing through supply channel 12 is normally held
by the Coanda effect in contact with a wall region 24, so that it
passes into a return channel 26, along which it can be returned to
the supply chamber. When controller 22 moves diverter member 20 to
its FIG. 2 active position, a portion of liquid flowing below
outlet opening 18 flows along the inner surface of the diverter
member due to the Coanda effect. The Coanda effect, also known as
"boundary layer attachment", is the tendency of a stream of fluid
to stay attached to a convex surface, rather than follow a straight
line in its original direction. The diverted liquid emerges from
the outlet opening due to the momentum of the liquid. Intermittent
pulsing movement of diverter member 20 will deliver individual
droplets 28 from the outlet opening 18.
It will therefore be apparent that each time diverter member 20 is
momentarily moved to its active position, a droplet of the liquid
is dispensed from the opening 18. The device can therefore be used
in ink jet printing, and a number of the devices can be assembled
side-by-side to form a printhead for dot matrix printing. This
permits the dispensing of very closely spaced fluid droplets. FIG.
3 is a detailed view of the dispenser of FIGS. 1 and 2.
Specifically, the lag time between activation of diverter member 20
and separation of the liquid drop from diverter member 20 is very
small, approximately equal to the ratio of the length of the
diverter member divided by the velocity of the liquid in ejector
channel 17. Preferably, the diverter member is no longer than, say,
ten microns and the fluid velocity is in the range of from five to
thirty meters per second. Accordingly, the time between activation
of diverter member 20 and separation of the liquid drop from the
diverter member is less than two microseconds. This corresponds to
a response frequency, which is defined as the inverse of the lag
time, of greater than 400 kHz. The energy to propel such droplets
derives from pump 16, typically located remotely from the
dispenser. Thus the dispenser and the printer so enabled are of the
continuous inkjet type and the response time characterizing the lag
between activation and drop ejection is very fast.
The dispenser may advantageously be micromachined from a block of
material or fabricated by electroforming, electroplating, chemical
etching or molding. Assembling separately-fabricated modules may
alternatively form it. The dispenser may be used for depositing
droplets for printing or for imaging applications, as well as other
nonprinting applications where there is a requirement for
dispensing precise volumes of fluids.
The dispenser of the present invention has a number of advantages
over known devices. The velocity of emission of the droplet will
directly depend on the supply pressure and not on control pressure,
and the dispenser can thereby yield drop velocities in excess of
twenty meters per second, which are much higher than those
achievable with previous piezo-electric and thermal systems. The
droplet size is controlled by the shape and position of the
diverter member and the velocity of the liquid, and not by the
dimensions of a nozzle. A dispenser in accordance with the
invention may operate with a velocity and throw distance that
exceeds those of previous devices. This enables deposits to be
effected on surfaces which are further from the dispenser, which is
required for industrial printing applications, such as printing on
cans, boxes, containers, and the like.
The present invention provides a monostable fluid control device,
which requires only a single ejector channel 17 without an
associated control channel. Actuation can be effected by any means
capable of imparting movement of the diverter member away from the
fluid stream and advantageously such means may be an actuator such
as thermal bimorphs as illustrated in FIG. 4 as 20a, piezoelectric
transducers as illustrated in FIG. 5 as 20b, or electrostatic or
magnetic transducers as illustrated in FIG. 6 as 20c with magnetic
coil 21.
As can be seen from FIGS. 1 and 2, diverter member 20 moves
mechanically in a direction substantially orthogonal to the fluid
flow or moves in a direction opposing fluid flow. Thus, the energy
to launch the drops does not come from the diverter member itself,
but comes instead from flow energy supplied by pump 16. This
contrasts with the source of energy imparted to drops disclosed by
the pressure increase mechanism of WO 95/1041 and U.S. Pat. No.
4,345,259 wherein energy is imparted to the ejected drops, as can
be appreciated by one skilled in fluid mechanics. Thus the energy
needed to activate the diverter member according to the present
invention can be very small relative to the energy used by
aforementioned prior art devices. In particular, for thermal
bimorphs, the calculated energy to move the tip of the bimorph from
its own equilibrium position to a position ten microns out of the
channel of FIG. 2 is typically less than 100 nJ for a motion that
releases drops of at least one pL volume. Thus the ejection energy
required per pL volume, a common measure of ejector efficiency, is
typically less than 100 nJ/pL. Piezo actuators can be more
efficient than thermal actuators because they require no energy
input to hold their actuated positions, as is well known in the art
of inkjet ejectors, and thus the ejection energy required per pL
volume for piezo actuators, such as those of FIG. 4, is calculated
to be less than 10 nJ/pL. These energies are additionally low in
cases for which the actuators remain in their actuated position for
a substantial time.
The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
PARTS LIST
10. dispenser 12. supply channel 14. supply chamber 16. pump 17.
ejector channel 18. outlet opening 20. diverter member 20a. thermal
bimorph dispenser 20b. piezoelectric transducer dispenser 20c.
electrostatic or magnetic transducer 21. magnetic coil 22.
controller 24. wall region 26. return channel 28. droplets
* * * * *